1/5x7+1/7x9+1/9x11+1/11x13+…+1/23x25
问题描述:
1/5x7+1/7x9+1/9x11+1/11x13+…+1/23x25
答
1/5x7+1/7x9+1/9x11+1/11x13+…+1/23x25
=1/2×(1/5-1/7+1/7-1/9+1/9-1/11+1/11-1/13+……+1/23-1/25)
=1/2×(1/5-1/25)
=1/2×4/25
=2/251/2哪里来的1/5x7=1/2×(1/5-1/7)1/7x9=1/2×(1/7-1/9)1/9x11=1/2×(1/9-1/11)1/11x13=1/2×(1/11-1/13)…………………………………1/23x25=1/2×(1/23-1/25)